Production of aromatic compounds



- Patented June -1 O, 1947 2,422,165 PRODUCTION OF AROMATIC COMPOUNDS James Kenneth Dixon, Riverside, Conn., assignor to American Cyanamld Company, New York, N. Y., a corporation of Maine No Drawing. Application August 21, 1945,

Serial No. 611,928

12 Claims. I

This invention relates to the production of aryl compounds having at least one aliphatic nuclear substituent which contains a carbon-to-carbon double bond, and more particularly, to the production of such arylcompounds as those which have a vinyl group attached to an aryl nucleus.

The patent of Murray Gray Sturrock and Thomas Lawe No. 2,373,982 which issued April 17, 1945, discloses a method of producing styrenes and other aryl compounds made in accordance with the present invention, and this patent deals with the use of siliceous catalysts, and more particularly, hydrated aluminum silicate catalysts.

An object of the present invention is to provide improved catalysts which are effective for the conversion of diaryl substituted paraflins, having at least two carbon atoms in the paraflin chain and having the aryl groups attached to the same carbon atom, into two aromatic compounds, including one which has an aliphatic nuclear substituent containing a carbon-to-carbon donble bond.

This and other objects are attained by employwhich comprises alumina and thoria at a tem-' perature of at least 350 C. and preferably at a temperature of about 500600 C. It is preferable that contact time be less than 0.4 second and in order. to avoid practical difilculties it is generally desirable to. employ a contact time of 0.001 second or more. Still anotherieature of the present process is the use of a diluent, preferably water vapor in relatively high proportions, namely, from about 5-150 or more mols oi diluent per mol of the diaryl substituted parafiln. Water vapor is one of the most desirable diluents since it may be easily condensed and thereby separated from the final product.

Example About 250 parts of a thoria-modified aluminum silicate catalyst (catalyst "11) are packed into a tube which is heated and maintained at a tem-.

2 perature between about 500 C. and about 550 C. Ditolylethane is mixed with water vapor and passed through the tube at the rate of about 360 parts per hour and water vapor is mixed therewith and fed at the rate of about 2960 parts per hour. The hydrocarbon condensate which is obtained after passage of the vapor through the tube is distilled to yield a light oil boiling below 200 C. and a heavy oil containing the unchanged ditolylethane and other substances, boiling at about the boiling point of ditolylethane including 1,1-di-p-tolylethylene. The light oil contains p-methylstyrene, toluene, and p-ethyltoluene each of which may be separated therefrom by fractionation, fractional crystallization or by a combination of fractionation and fractional crystallization. The ethyltoluene may be used for any desired purpose and, for example, it may be dehydrogenated to form p-methylstyrene. The unreacted ditolylethane may be passed through the reaction tube in the same manner as described above, in order to convert additional quantities thereof, to other aromatic'compounds, including p-methylstyrene. In this way, a high yield of p-methylstyrene, based upon the ditolylethane consumed and lost, is obtained when due credit is given for the conversion to toluene and ethyltoluene. 1

If the highbolling oil contains suflicient ditolylethylene to warrant separation, this may be done by fractionation, hr by fractional crystal-- Preparation of catalyst A About 454 parts of purified sodium silicate (Na2S i03.9H2O) are dissolved in about 1600 parts of water and 20% sulphuric acid is added slowly with vigorous agitation until the pH of the re- .sulting silica gel suspension is about 6.5. The

agitation iscontinued for about 2 hours and the el is then filtered and reslurried in about 3500 parts of pure water. The gel ,is again filtered and suspended in about 3500 parts of water a total of five times. The gel is finally filtered and slurried twice in about 3500 parts of 0.01M HCl and then with the pur water threetimes. After this the gel is filtered and dried at 110 C. .and

then heated to about 700 C. for one-half hour.

About parts of the silica gel prepared in accordance with the foregoing procedure is broken intopieqes about 0.2 cm. in thickness and'mixed 3 with about 225 parts of an aqueous solution containing 184 parts of A1(NO)3.9H2O and 52 parts. of Th(NO3) 4.4H20. This mixture .is agitated from a few minutes 'to about one-half hour after which it is filtered to remove excess water. The

resulting product is dried atabout 110 C. and ignited at about 500 C. in the presence of steam. The final product contains about 5% A120: and 5%, T1102.

,The thoria-modified aluminum silicate catalyst used in accordance with this invention may be prepared by co-precipitation of alumina, thoria and silica to form a hydrogel which is thereafter washedand dried. Still another method of preparation is to precipitate thoria on an aluminum silicate, or to precipitate the alumina on a thorium silicate. It ispreferable that the gels less than-0.4 second. The contact times between about 0.1 and 0.05 are especially suitable. Generally it. is desirable to employ a contact time of 0.001 second or longer, in order to avoid practical diiilculties. The calculation of the contact of the vapor with the catalyst is a complex matter, and in order to simplify this calculation I have used the term fcontact time herein to mean those values which are computed on the assumption that the catalyst contains 50% voids and neglecting both the pressure drop through the catalyst and the increase in volume which occurs during the reaction. The contact time employed in the foregoing examples is about 0.1

be calcined after drying, for example at a tem- 4 portion of alumina.

My catalysts may include otherheat-resistant and solid substances which activate them, or which are entirely inert, and such substances may be used to extend the active surface of the thoria-modified alumina silicate catalysts, or they may be used as supports for the catalysts. For example, the thoria-alumina-silica catalysts second. Inasmuchas the reaction is neither highly exothermic nor endothermic it is not necessary to supply much more heat than that necessary to compensate for conduction and radiation losses in order to maintain the reaction temperature of the vapors passing through the catalyst, providing that the vapors which are fed to the catalyst are preheated to about the desired reaction temperature and.providing a high ratio of diluent of this invention may be supported upon-finely 1 divided silicon carbide, non-porous aluminum ox-' ide (such as those materials sold under thetrade names Alfrax, Alundum, etc.), highly fired ceramic materials in the form of rings, saddles and the like. Binding agents such as sodium silicate may be advantageously employed in some cases to improve the mechanical stability of my catalysts.

My catalysts are employed in a finely divided erably no larger than about 5 mms. in their greatest diameter. The pellets may be in any desired shape such as cubical, spherical, or of an irregular granular shape. When large pellets are employed the vapor velocity varies widely between the center and outside of the pellet, and therefore the contact time at the center of the pellet is longer than desirable. It is preferable that the particles be as fine as possible in order to reduce the diflcerenc'e betweenthe maximum and minimum vapor velocities which occur in the catalyst bed. Obviously the particle size should not be so small that the catalyst packs thereby causing the va-- ppm to channel through the catalyst instead of passing therethrough in a uniformma'nner.

The converter into which the-catalystis packed. may be a tube constructedof'steel;"silica' or any other suitable material and in large'scalebperaitions the converter may comprise aplura1ity'0f such'tubes or it maybe ashell-type converter having oneor more'layers or trays of catalyst therein.-- U

A short contact time ofthe diaryl parafiin with the-catalyst is" desirable in'carrying out the reactions in accordance with this invention. While longer contact times may be used if desired it is generally preferable that the contact time be condition fashioned into pellets whichrare pref- 81108 heaters.

to the diaryl paramn is employed. I therefore prefer that the vapors fed to the catalyst be preheated to the reaction temperature. .Any suitable method of heating the converter may be employed such as, for example, electrical resist- The following are illustrative of the aliphatic compounds having two aryl substituents attached to the same carbon atom thereof which may be converted into themononuclear aromatic comounds in accordance with the present invention: 1,1-dlphenylethane, each of the l-phenyl-1-tolyl-- ethanes, each of the 1,1-ditolylethanes, each of the l-phenyl-l-xylylethanes, each of the l-tolyll-xylylethanes, each of the 1,1-dixylylethanes, 1,1- diphenylpropane, each of the l-phenyl-l-tolylpropanes, each of the 1,1-ditolylpropanes, each of the l-tolyl-l-xylylpropanes, each of th 2,2- ditolylpropanes, each of the l,1-di-(monochlorophenyl)-ethanes, each or the 1,1-di-(di chl01'0- phenyl)-ethanes, each ofthe 1,1-di-(monohydroxy phenyl) -ethanes, each of the 1,1-dicresylethanes, each of the 2,2-dicresylpropanes, each of the 1,1-dinaphthylethanes, each of the l,l-,di-'

,xenylethanes, each of the l-tolyl-l-naphthylethanes, and the like and their nuclear substituted h'alogen, hydroxyl and other derivatives all of which are volatile at the temperature and pressure used in the process. Those substances containing tolyl, xylyl, cresyl, xenyl, monochlorophenyl and dichlorophenyl groups may be attached to the carbon atom of the paraflin chain at the ortho, meta or para positions and when twoof these groups are present they may be attached in the same or different positions.

The reaction temperature may be varied from about 350 C. up to about 600 C. or even higher in some cases. Temperatures above 600 C. cause some pyrolysis loss but on the other hand some of the diaryl paraffins are not easily decomposed at lower temperatures. It' is particularly important to employ a short'time of contact when temperatures in the neighborhood of 600 C. are used in order to avoid an undesired amount of pyrolysis loss due to side-reactions. Among such sidereactions are those-which lead to the formation of polynuclear compounds including anthracene derivatives.

One of the. advantages of employing a short contact time with catalysts is that the life thereof is prolonged. With contact times of the order of 1 second or more the catalyst may become should be raised to about 500-650 C. The air enables the carbon to burn whereas the steam or carbon dioxide which is used in conjunction with the air keeps the temperature from rising too high which might cause a reduction in the activity in the catalyst. Generally, at temperatures of about 500 C. the carbon begins to burn off and the heat of this reaction causes the temperature to rise to about 650 C. without the application of any external heat.

It may be seen that the proximity of the reactivation temperature to the reaction temperature greatly simplifies the change from normal operation to reactivation-and back to normal operation. Since the normal highly active life of the catalyst greatly exceeds the time required for its reactivation the operation of two or more converters in parallel is readily accomplished. The short time of reactivation enables one to keep one or more converters in normal operation while one or more other converters are being reactivated.

Any material which is volatile and which does not react with the diaryl substituted paraffin which is to be used in accordance with my process and which does not react with the products formed by the decomposition of the diaryl substituted paraflin may be used as a diluent. Among these, some examples are: water, the hydrocarbons (such as benzene. and toluene), the fixed gases (such as nitrogen and carbon dioxide), etc. Water vapor is the preferred diluent inasmuch as it may be readily condensed and therefore separated from the products of the reaction, whereas the fixed gases or the hydrocarbons are somewhat more difiicult to separate from the product and such separation requires higher expenditures than are required for the separation of water from the product. Water vapor also has an additional advantage in that it may maintain the catalyst in highly active form.

One of the most important reasons for the use of a diluent is that the. time of contact .of the diaryl substituted parafiin with the catalyst can be reduced to the desired point easily. It has been found that in order to obtain the short contact times which are desirable in accordance with the present invention the molal ratio of diluent to the diaryl substituted aliphatic compound in the feed to the catalyst is'preferably between about 5:1 and 150:1, Or more. If the feed can' be supplied rapidly enough to provide a low contact time without the use of the large proportion of diluent the ratio of diluent to the diaryl substituted paraffin may be as low as 1 :2.

It has been found that it is frequently desirable to convert only a few percent of the diaryl substituted paraflin fed to the catalyst in one pass but by recovering the unconverted diaryl substituted paraflin and recirculating it from one to five times-or more, a high yield is obtained very economically.

My process may be operated at elevated or reduced pressure and under some conditions it may be particularly advantageous to operate under reduced pressure. If the diaryl substituted paraflln which is to be used in accordance with prescut processes is not readily volatile at ordinary pressure, reduced-pressures may be used to facilitate the operation of my process.

The present process is a convenient and economical method of converting the diaryl substituted paratfins, having at least two carbon atoms in the paraffin chain and having the two aryl groups attached to-the same carbon atom, into two aromatic compounds, one of which contains a side chain having an ethylenic group. The vinyl substituted aryl compounds prepared in accordance with the present invention have wide utility in the production of polymers which in turn are useful for molding, casting, laminating and for many other purposes. Furthermore, pure aryl compounds such as xylene in extremely high purity may be produced simultaneously with the production of the aromatic compound containing an ethylenic side chain. Thus when a diaryl substituted paraffin is cracked in accordance with this invention one molecule of an aryl compound having an ethylenic side chain is obtained together with one molecule of a pure aryl compound which does not have an ethylenic side chain. Such pure aryl compounds, as for example pure m-xylene or pure p-xylene, findutility in the synthesis organic compounds where the presence of one or more of the possible isomers is undesired.

I claim:

1. A process of producing a plurality of aromatic compounds which comprises heating a paraffin having at least two carbon atoms and having two aryl substituents attached to one of said carbon atoms at a temperature which will cause said paraifin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C. in the presence of a thoria-alumina-silica catalyst.

2. A process of producing a plurality of; arcmatic compounds which comprises contacting a substance selected from the class consisting of paraffins having at least two carbon atoms in the paraffin chain and having two aryl substituents attached to one carbon atom thereof, and their nuclear substituted derivatives, at a temperature which will cause said paraflln to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C. with a thoria-alumina-silica catalyst which promotes simple molecular decomposition into two aromatic compounds.

3. A process of producing a plurality of arcmatic compounds which comprises mixing a substance selected from the class consisting of diaryl substituted paraffins having at least two carbon atoms in the paraifin chain and in which both aryl groups are attached to the same carbon atom and their nuclear substituted derivatives with a diluent, contacting the resulting mixture thereof with thoria-alumina-silica catalyst and maintaining the. temperature of said mixture at a temperature which will cause said paraffin to decompose into a plurality. of aromatic compounds in the presence of a catalyst and which is at least 350 C. during the time it is in contact with said catalyst. I

4. In a method of producing mononuclear aromatic compounds, the steps which comprise heating one of a class of substances consisting of asymmetric diarylethanes, the aryl groups of which are mononuclear, and their nuclear substituted derivatives at a temperature which will cause said paraflln to decompose into a plurality of aromatic compounds in the presence of a 7 catalyst and which is at least 350 C. passing the resulting heated substance through a thoriaalumina-silica catalyst. which promotes simple molecular decomposition together with a diluent, at such a rate as to provide a contact time with the catalyst of between about 0.001 second and about 0.4 second.

5. A process as in claim 4 wherein said diluent is water vapor.

6. In a method of producing a plurality of arcmatic compounds the steps of which comprise heating a substance of the class consisting of diaryl substituted paraflins having at least two carbon atoms in the paraffin chain and having both aryl groups attached to one of the carbon atoms, and their nuclear substituted derivatives, to a temperature which will cause said paramn to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350" C. passing said substance through a thoria-alumina-silica catalyst with a contact time of less than 0.4 second.

7. In a method of producing a plurality of arcmatic compounds the step which comprises contacting asymmetric diarylethane with a thoriaalumina-silica catalyst at a temperature which will cause said paraflin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C. and for a contact time of less than 0.4 second 8. In a method of producing a plurality of aromatic compounds the step which comprises contacting an asymmetric ditolylethane with a thoria-alumina-silica catalyst at a temperature which will cause said paraflin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C. and for a contact time of less than 0.4 second.

9. In a method of producing a plurality of arcmatic compounds the step which comprises contacting a 1,1-di-xylylethane with a thoria-alumina-silica catalyst at a temperature which will 10. In a process of producing a plurality of aromatic compounds, the step which comprises cause said parafiln to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C. and for a contact time of less than 0.4 second.

contacting an asymmetric diarylethane with a thoria-alumina-silica catalyst at a temperature which will cause said paraflln to decompose into a plurality of aromatic compounds in the presence of a catalyst and which isat least 350 C. and for a contact time-oi less than 0.4 second, 'said diarylethane having at least one aryl group substituted with an alkyl group,

11. In a process of producing a plurality of aromatic compounds, the step which comprises contacting an asymmetric diarylethane with a thoria-alumina-silica catalyst at a temperature which will cause said paraflln to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C. and for a contact time of less than 0.4 second, said diarylethane having at least one aryl group substituted with a hydroxyl group.

12. In a process of producing a plurality of aromatic compounds, the step which comprises contacting an. asymmetric diarylethane with a thoria-alumina-silica catalyst at a temperature which will cause said parafiin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C.

and for a, contact time of less than-0.4 second, said diarylethane having at least one aryl group substituted with an alkyl group and a hydroxyl group.

JAMES KENNETH DIXON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,373,982 Sturrock et al, Apr. 17, 1945 2,214,455 Eglofl et al Sept. 10, 1940 Dreisbach May 12, 1942 OTHER REFERENCES Sheibley et al., Jour Am. Chem. Soc., vol. 62, 840-1 (1940), Pat. Ofl. Lib. 

